The present invention relates to a method for operating a longitudinal driver assist system of an automobile, in particular in ACC (adaptive cruise control) system, as well as to an automobile with a driver assist system configured to carry out the method.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Longitudinal driver assist systems for automobiles are known since some time. They control, based on appropriate braking and acceleration interventions, the distance, mostly in form of a time gap, from an automobile in front. The best-known example for such driver assist systems, also referred to as distance control systems, is the so-called ACC systems (Adaptive Cruise Control). These systems have in common that information forming the basis for the control of the distance and speed of an automobile driving directly in front is obtained from at least one sensor, in particular in a radar sensor and/or a video camera. This function is combined in ACC systems with an automatic speed control.
Problems may arise when several automobiles which are each equipped with a longitudinal driver assist system, in particular an ACC system, drive behind one another in a convoy, for example in stop-and-go traffic, in particular in city traffic. Although it can be assumed that the first two automobiles driving behind one another with an active driver assist system can follow each other under harmonic control, the longitudinal guidance may no longer function properly when a third automobile is added.
In particular during deceleration phases before a complete stop, for example when approaching a red traffic light, the system limits of the longitudinal driver assist system may be exceeded if the aforementioned problems exist, requiring manual intervention if the driver assist system is no longer capable to ensure an operative longitudinal guidance. However, the controller may start to “oscillate” when traveling in longitudinal convoy also in a typical low-speed operation, in particular in a stop-and-go operation, producing a type of accordion effect and causing an inefficient driving behavior (strong acceleration and strong braking). In this situation, the stability of actual longitudinal driver assist systems, in particular ACC systems, in a convoy can no longer be guaranteed.
These undesirable effects are caused, for example, by the delay times of the sensor system and the actuator system and by the time constants of the longitudinal guidance (longitudinal control), in particular by preset, predetermined gradients of the speed and the like or gradients located in a certain range. Delays in the technical field of sensors are mostly due to the type of the evaluation, when for example data are first made plausible or otherwise thresholds aiding in the safety of the detection must be overcome. The time constants of the longitudinal control of a longitudinal driver assist system are parameterized particularly by taking into account the driving comfort encountered in frequently occurring and typical traffic situations.
Time delays and time constants also occur in convoys where the vehicles are operated by human drivers; however, these delays and time constants are far less pronounced, because humans are able to recognize, evaluate and react and hence also drive with substantially more foresight than would be possible with actual driver assist systems. In addition, a “build up” in short convoys is much less likely, because the time delays and the time constants also do not match each other.
It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved control method which reduces, and potentially completely eliminates, problems in a longitudinal driver assist systems during travel in a convoy.